The Guerbet reaction is an important organic synthesis reaction as a process of producing a dimeric alcohol by dimerizing a starting-material alcohol. The mechanism of this reaction is thought to be as shown in the following reaction scheme 1. Namely, the reaction is thought to proceed on the basis of a combination of three reactions, i.e., a reaction in which a starting-material alcohol is caused to undergo a hydrogen abstraction reaction (hydrogen transfer reaction) using a basic compound and a complex of a transition metal with a phosphine compound to thereby yield the corresponding aldehyde intermediate, a reaction in which the aldehyde intermediate is dimerized by an aldol condensation reaction into an α,β-unsaturated aldehyde intermediate, and a reaction in which the α,β-unsaturated aldehyde intermediate undergoes a hydrogenation reaction (hydrogen transfer reaction) and thereby becomes a dimeric alcohol (non-patent document 1 and non-patent document 2).

A process of dimeric-alcohol production based on the reaction mechanism has been applied to higher-alcohol production in which starting-material alcohols having 6 or more carbon atoms are used to obtain dimeric alcohols having 12 or more carbon atoms. These higher alcohols are used mainly as raw materials for cosmetics, emulsifying agents, etc.
However, there has been no case in which that reaction mechanism is applied to a starting-material alcohol having 4 or less carbon atoms. For example, there has been no case in which the starting-material alcohol is ethanol, which has 2 carbon atoms, and n-butanol is produced as a dimeric alcohol therefrom. This is because the yield of the n-butanol obtained and the selectivity to n-butanol are low and the reaction is not industrially advantageous. There has been a desire for a process of n-butanol production in which n-butanol is produced in high yield with high selectivity using a smaller amount of a catalyst.    Non-Patent Document 1:J. Mol. Catal. A: Chem., 2004, 212, p. 65    Non-Patent Document 2:J. Org. Chem., 2006, 71, p. 8306